Cheap LED light string - will this work?

I ordered one of those cheap LED light strings that has like 30 small LEDS, I assume in parallel. They are powered by a couple of AA cells. I am going to assume that this setup is direct drive. What I was wondering is if I used one 14500 cell and one dummy cell if that would be too much voltage. Anyone have any experience doing something like this?

It's not really important because I have plenty of NiMh AA cells around, but I think the lower voltage compared to primary cells might either not fire the LEDs at all, or not last long.

I find that the red, yellow, and green 5mm LEDs tend to require about 2.2v to power them at their peak 20mA current. If you have any white or blue LEDs in that string, they require about 3.0v. I kind of doubt your string has blues or whites, unless it has a boost driver built in to power them from 2xAA cells (or it won't last long before the voltage drops too much).

I'm betting that your string doesn't even have any resistor in it, and just relies on the voltage sag of alkalies and the resistance of the wires to limit current. It could be using up to 600mA of current, though it's probably less.

So, sticking in a low-resistance lithium-ion 4.2v battery is likely going to be too much. It might work, for awhile, but the LEDs could burn out.

At the very least, you'll probably have to wire in a resistor in series with your lithium-ion battery, to limit current. Something around 3 ohms? It will be a big waste of energy, though, and you'll need something that can handle about 1.5 watts.

Stick with AA's, and I'm betting NiMH will be fine.

Thanks for the info. Once I read it I realize that it was already stored somewhere back in the attic of my mind. That explains why some of the Photon Micro colors could use one 2032, while the others had to use two 2016s.

I guess I'll just stick with the AAs.

It's very doubtful even a string of 10 LEDs could get away with current limiting by internalbattery resistance running from AA or AAA cells. It might work for 1 LED with one or twoLithium 2016 or 2032 cells. Dollar-store 10-strings tyically have a 1/4W series resistor less then 10 ohms to a few tensof ohms depending of number of LEDs colour and (importantly) number of cells (2 or 3). Some have electronics e.g. timers but are still direct-drive so likely use current regulationwith a set resistor, though I have not investigated in detail. 4V to a 2-cell string may not cause damage but brightless and battery life will be factors. Ifusing a Li-ion with 2-cell, could insert a diode instead of shorted cell though efficiency suffers.Either that or increase the resistor value if you can get to it. I have a variety of different strings running on everyone else's used alkalines, virtually limitelesssupply from recycling bins (some are virtually unused). I am at the other end, running at lowervoltages, so 3-cell strings work better.Dave

Okay, I finally got around to opening the box. The battery case has a timer associated that will shut the lights off after six hours. So I have a choice of On, Timer, and Off. The tiny circuit board has what I take as a cap on one side, and two little black bar things on the other. One is labeled 288 as far as I can tell, and the other is smaller and is also labeled 2something. Now to go hunt up three AAs and see what it looks like.